Biochemical and physiological processes in multicellular animals require the coordinated interactions of many cells. Maintenance of these cell-cell associations of the specific cell junctions which arise from them is the basis of tissue function. The purpose of this Project is to determine the role of one specific embryonic cell surface constituent in the control of retina cell-cell recognition, and in the development of neuronal connections. We have purified this constituent, the neural retina cognin; it is a glycoprotein which enhances the reaggregation of dissociated chick and mouse neural retina cells in vitro. Scanning electron microscopy localization of the cell surface cognin suggests that its distribution in the retina, on differnt retina cell types, and the changes in such a distribution during development, may be significant in elucidating the role of cognin in vivo. We propose, first, to identify other cell surface molecules which must interact with cognin, and to thereby reconstruct the mechanism of cell-cell recognition. This will be done by affinity chromatography to identify molecules which bind cognin, and by studying a simple model system, the in vitro interaction of membranevesicles prepared from retina cells. We will also utilize the available polydeterminant antibody to cognin to determine the localization of cognin in vivo. This will be compared to the distribution of cognin on cell types isolated from the retina by density gradient fractionation in order to determine the possible role of cognin in two critical morphogenetic phases of retina development. These are; the early inductive interactions between retina and other optic area tissues, and the development of the stratified architecture of the mature retina. Finally, we propose to test a specific hypothesis that cognin plays a role in the development of synapses later retinogenesis.